Tower: "SBA maintain runway heading, climb to 4000 ft, cleared for takeoff"
SBA read back and commenced opening throttles
Unknown: "foxtrot"
SBA: "confirm we are cleared for takeoff"
Tower: Negative, hold your position
Turned out our clearance was cancelled and TFF (an F27) was cleared for takeoff opposite direction runway. Due to a large hump in the runway, limited vis from either end. The "foxtrot' was the last letter of TFF acknowledging takeoff clearance. We did not copy that because of reading back SBA (DC3) clearance.
In 1943, my father was bumped from a DC3 observation flight and the aircraft collided with another with no survivors. In 1970 I was again lucky (and vigilant) at the same place - the old Port Moresby airport.
Who out there in pprune land delay takeoff for a single "foxtrot"?